The present invention relates to lock cylinder assemblies. More particularly, the present invention relates to lock cylinder assemblies that may be reprogrammed without removing the cylinder plug. Most particularly, the present invention relates to a master keying system and method for programmable lock cylinder assemblies.
FIGS. 71A through 71C show a typical pin tumbler cylinder 510. The cylinder 510 consists of a shell 512 having a rotatable plug 513 within. The plug 513 has an axially extending keyway 514, which accepts key 515. A series of cuts 516 are placed on the upper edge of key 515. Within the shell 512 and plug 513 are a plurality of pins 520 and springs 521. Pins 520 are comprised of at least two segments, a bottom pin 520a and a top pin or driver 520b. When a cylinder has been pinned for master keying, one or more master pins 520c (see FIGS. 71D and 71E) are used in each pin stack. The depths of the cuts 516 on the key 515 are called bittings and typically are numbered from 0 to 9. With no key 515 inserted in the cylinder 510, the top pins 520b and bottom pins 520a are forced by the springs 521 down into the plug 513. The top pins 520b are then partially in the shell 512 and partially in the plug 513, forming an obstacle that keep the plug 513 from turning, as shown in FIG. 71A. When a proper key 515 is inserted into the cylinder 510, the bitting depth of the cuts 516 brings the top of each of the bottom pins 520a exactly to the surface of the plug 513, forming a shear line 524, as shown in FIG. 71B. With the tops of the bottom pins 520a aligned with the shear line 524, the key 515 and the plug 513 can be turned. When an incorrect key 515 is inserted, one or more of the top and bottom pins 520b, 520a will not align with the shell 512 surface to form the shear line 524, thereby preventing rotation of the key 515 and plug 513, as shown in FIG. 71C.
FIGS. 71D and 71E illustrate a typical cylinder 510 which has been pinned for master keying. The term “master keyed” usually denotes that each individual cylinder is operated by two or more different keys. The key that normally opens only one cylinder or keyed alike group of cylinders is called a change key. The key that opens all the cylinders in a group or series is called a master key. An example of a simple master key system would be in a small office building. There would be an individual change key for each office door, and there would be a master key to operate all office doors. The essential difference between an ordinary pin tumbler cylinder and a master keyed cylinder is the use of master pins 520c. A master pin is an additional top pin, usually shorter, which is inserted between the bottom pin 520a and the top pin 520b. In each pin chamber where a master pin 520c is located, a second shear position is created. The cylinder can be operated at either shear position. Thus, different key bittings can be used for each position where there is a master pin. FIG. 71D shows a master keyed cylinder 510 with a change key 515 inserted and FIG. 71E shows the same master keyed cylinder 510 with a master key 515 inserted. In both figures, the pins 520 have aligned to form a shear line 524, thereby permitting the key 515 and plug 513 to rotate.
When reprogramming a lock cylinder 510 using a traditional cylinder design, the user is required to remove the cylinder plug 513 from the cylinder body 512 and replace the appropriate pins 520 so that a new key can be used to unlock the cylinder 510. This typically requires the user to remove the cylinder mechanism from the lockset and then disassemble the cylinder to some degree to remove the plug 513 and replace the pins 520. This requires a working knowledge of the lockset and cylinder mechanism and is usually only performed by locksmiths or trained professionals. Additionally, the process usually employs special tools and requires the user to have access to pinning kits to interchange pins 520 and replace components that can get lost or damaged in the reprogramming process.